Question

A Plano convex lens (f=20cm) is silvered at plane surface. Now it's focal length will be

Answer 1

its fucal length will be 10cm and it will act as a concave lens

Answer 2

Answer:

A Plano convex lens is silvered at plane surface. It's focal length will be 10 cm.

Explanation:

Given that,

Focal length of lens f= 20 cm

Using formula for focal length

$\dfrac{1}{F}=\dfrac{2}{f}+\dfrac{1}{f_{m}}$

Now, Plano convex lens silvered on plane surface has $f_{m} =\infty$

Put the all values into the formula

$\dfrac{1}{F}=\dfrac{2}{20}+0$

$\dfrac{1}{F}=\dfrac{1}{10}$

$F = 10\ cm$

Hence, A Plano convex lens is silvered at plane surface. It's focal length will be 10 cm.